Problem: $ { {-1} \times \left[\begin{array}{rr}{4} & {0} \\ {-1} & {3} \\ {2} & {-1}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-1}\times{4} & {-1}\times{0} \\ {-1}\times{-1} & {-1}\times{3} \\ {-1}\times{2} & {-1}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-4} & {0} \\ {1} & {-3} \\ {-2} & {1}\end{array}\right]}$